Field of the Invention
The present invention relates to a movement joint, in particular of the type used in the laying of concrete, remaining in place thereafter and allowing free movement of concrete slabs on opposite sides of the joint.
Description of the Related Art
Movement joints are provided between concrete slabs to allow them to separate at intended joint lines as the concrete shrinks on curing after laying.
Many joints include a divider between adjacent slabs and against which concrete is poured. In this respect, the joints perform the function of concrete shuttering. In this specification, we refer to such a joint as a “construction joint”. In a construction joint the divider will be suited to the nominal depth of the concrete. It may not be the full depth of the slabs in that the sub-base on which the concrete is laid may not be sufficiently level for the divider to abut the sub-base along the entire length of the joint. In such situation, some concrete can be expected to pass under the divider, but the depth will be sufficient for the concrete to be tamped level with the top of the joint.
The edges or arrises of the concrete at a joint require support against spalling, that is breaking off in shear and/or impact as from forklift truck tyres.
Many forms of arris protection have been used. One early example, left in situ from casting, was the use of angle irons set up on wooden shuttering.
More recently strip steel on edge has been used, anchored into the concrete, normally by means of a number of studs angled down and extending towards the body of the slab. A typical construction joint of this type is shown in our patent application No EP 1,867,783. It's abstract is:                “Apparatus for forming the edge of a concrete floor slab, the apparatus comprises a divider plate formed with a plurality of apertures, dowels for engaging through the apertures and sleeves for applying to the dowels, in which the divider plate is provided with means, in use, to adjust the height thereof above the ground. The height-adjustment means comprises a removable jack.”            In this joint, known as our Alpha Joint, we provided a pair of arris protection rails, one welded to the top of the divider plate and the other frangibly connected to the one. Each was provided with spaced anchor bolts for anchoring the rails to their concrete slabs. The arris rails being of square section had good anti-spalling action.
Despite providing a good measure of protection against spalling, this joint has an inherent problem in that, wherever a joint is straight and has opened to tens of millimeters, due to tyres, typically of a fork lift truck having solid tyres and little or no sprung suspension, dropping partially into the opening and striking against the opposite side of the joint. The resulting impacts are liable to cause eventual deterioration of the joint.
Various arrangements have been provided for further reinforcement of the arrises including plates set flush with the surface of the concrete, as developments of the use of angle irons. Amongst these developments are plates extending across the opening in the joint. Further, these plates can have interdigitated edges, whereby a tyre passing across the joint encounters a sinusoidal gap between the plates. This is advantageous in preventing the simultaneous impact across the width of a tyre passing over the gap.
Such sinuosity has been provided not only in horizontal plates but also in arris members extending down from the surface of the concrete having the joint. These sinusoidal arris members have been mounted on top of vertical members extending lower into the joint. This makes for cost and complexity in fabrication.